Skip to navigation

⌂ ∞ ▽ Revs on the BBC Micro

Text: PrintToken

       Name: PrintToken                                              [Show more]
       Type: Subroutine
   Category: Text
    Summary: Print a recursive token
  Deep dive: Text tokens

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * GetMenuOption calls PrintToken
             * GetWingSettings calls PrintToken
             * MainLoop (Part 1 of 6) calls PrintToken
             * MainLoop (Part 2 of 6) calls PrintToken
             * MainLoop (Part 3 of 6) calls PrintToken
             * MainLoop (Part 5 of 6) calls PrintToken
             * PrintDriverPrompt calls PrintToken
             * PrintDriverTable calls PrintToken
             * PrintHeader calls PrintToken
             * PrintRaceClass calls PrintToken
             * SetScreenMode7 calls PrintToken
             * WaitForSpaceReturn calls PrintToken




 Addresses of token strings are in the (tokenHi tokenLo) table. Tokens are
 numbered from 0 to 54.

 Each token's string contains bytes that are printed as follows:

   * 0-159     Print character n
   * 160-199   Print n - 160 spaces (0 to 39)
   * 200-254   Print token n - 200 (0 to 54)
   * 255       End of token



 Arguments:

   X                    The token number (0 to 54)

   (xCursor, yCursor)   The on-screen position for the token



.PrintToken

 LDY #0                 \ We are about to work our way through the token, one
                        \ byte at a time, so set a byte counter in Y

.toke1

 LDA tokenHi,X          \ Set (S R) = the X-th entry in (tokenHi tokenLo), which
 STA S                  \ points to the string of bytes in token X
 LDA tokenLo,X
 STA R

.toke2

 LDA (R),Y              \ Set A to the Y-th byte at (S R), which contains the
                        \ next character in the token

 CMP #255               \ If A = 255 then we have reached the end of the token,
 BEQ toke8              \ so jump to toke8 to return from the subroutine

 CMP #200               \ If A < 200 then this byte is not another token, so
 BCC toke5              \ jump to toke5

 SEC                    \ A >= 200, so this is a pointer to another token
 SBC #200               \ embedded in the current token, so subtract 200 to get
                        \ the embedded token's number

 STA T                  \ Store the embedded token's number in T

 TXA                    \ Store X and Y on the stack so we can retrieve them
 PHA                    \ after printing the embedded token
 TYA
 PHA

 LDX T                  \ Set X to the number of the embedded token we need to
                        \ print

 CPX #54                \ If X <> 54, jump to toke3 to skip the following three
 BNE toke3              \ instructions and print the embedded token

 LDX #0                 \ X = 54, so call PrintHeader with X = 0 to print
 JSR PrintHeader        \ "FORMULA 3  CHAMPIONSHIP" as a double-height header
                        \ at column 4, row 3, in yellow text on a red background

 JMP toke4              \ Skip the following instruction

.toke3

 JSR PrintToken         \ Print token X (so if it also contains embedded tokens,
                        \ they will also be expanded and printed)

.toke4

 PLA                    \ Retrieve X and Y from the stack
 TAY
 PLA
 TAX

 INY                    \ Increment the byte counter

 JMP toke1              \ Loop back to print the next byte in the token, making
                        \ sure to recalculate (S R) as it will have been
                        \ corrupted by the call to PrintToken

.toke5

                        \ If we get here then A < 200, so this byte is not
                        \ another token

 CMP #160               \ If A < 160, jump to toke6 to skip the following three
 BCC toke6              \ instructions

 SBC #160               \ A is in the range 160 to 199, so subtract 160 to get
                        \ the number of spaces to print, in the range 0 to 39

 JSR PrintSpaces        \ Print the number of spaces in A

 BEQ toke7              \ Skip the following instruction (this BNE is
                        \ effectively a JMP as PrintSpaces sets the Z flag)

.toke6

 JSR PrintCharacter     \ Print the character in A (which is in the range 0 to
                        \ 159)

.toke7

 INY                    \ Increment the byte counter

 JMP toke2              \ Loop back to print the next byte in the token

.toke8

 RTS                    \ Return from the subroutine